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Size effect of concrete in compression, State-of-the–Art

Author: Gro Markeset | Size: 2.4 MB | Format: PDF | Publisher: SINTEF | Year: 2008 | pages: 33 | ISBN: 978-82-536-1009-2

Size effect is known as a relative change (decrease) of the structural properties (peak
resistance, ductility, etc.) when the structure size increases. In quasi brittle materials such as
concrete, this is a recognized phenomenon.
For the concrete material most focus on size effect has been connected to the tensile states of
stress. After the development of the Fictitious Crack Model (Hilleborg et al 1976), there have
been large research activities within the field of fracture mechanics applied for concrete,
particular for tensile states of stress. Based on this work it is now generally accepted that
tensile failure is localized to a limited zone and that this failure localization is the source of
the so-called size effect. In the new Eurocode 2 this size effect is implemented for punching
and shear using a size factor k= 1+ 200 / d , where d is the member depth in mm.
Compressive failure is, as in tensile failure, found to be localized to certain zones and gives
rise to a size effect (Hillerborg (1988), Bažant (1989), Markeset (1993, 1994), Markeset and
Hillerborg (1995), Bigaj and Walraven (1993), Janson and Shah (1997), Walraven (2007),
van Mier (2007)).
The compressive behaviour of concrete is one of the fundamental parameters of structural
design as most load-bearing concrete elements, such as beams, columns and slabs, experience
compressive strain gradients where the compressive strain at the critical section is in the postpeak
(softening regime) of the stress-strain curve at failure. The presently used codes of
practice do not limit their application field to some selected range of member dimensions
although experimental studies have shown that size effect of concrete loaded in compression
exists.
In this report the size effect of compressive failure of concrete members exposed to uniaxial
compression as well as compressive strain gradients is discussed.

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